The present invention relates to a three-dimensional photonic crystal light emitting device such as a light-emitting diode (LED) or a laser diode (LD), which includes a three-dimensional photonic crystal and emits light by injecting an electric current into an active medium.
A general conventional semiconductor light emitting device is constituted of a P-cladding layer, an active layer and an N-cladding layer. The semiconductor light emitting device is injected with holes from an electrode through the P-cladding layer to the active layer. On the other hand, the semiconductor light emitting device is injected with electrons from an electrode through the N-cladding layer to the active layer. The holes and the electrons recombine together in the active layer to emit spontaneous emitted light having energy corresponding to a band gap of the active layer. In particular, when a resonator is formed with a cleaved surface so as to include an active layer, the semiconductor light emitting device generates stimulated emitted light due to a light-amplification by the resonator to generate a laser beam.
As a technique to increase luminous efficiency of an LD, a technique to increase carrier injection efficiency by lowering electric resistance, a technique to reduce a loss in a recombination process other than that in stimulated emitted light, and a technique to decrease leakage light by enhancing optical confinement are proposed.
Japanese Patent Laid-Open No. 2003-198045 discloses a configuration of an LD in which part of a P-cladding layer is replaced with an N-type material, and a tunnel junction layer is disposed between the P-type material and the N-type material to lower electric resistance. However, this configuration is incapable of enhancing the optical confinement, and incapable of reducing a loss in the recombination process.
On the other hand, there has been proposed, as a method of reducing a loss due to recombination which brings emission of light other than light at a desired wavelength, a method of controlling spontaneous emission by a photonic crystal to obtain high luminous efficiency (refer to “Physical Review Letters, Vol. 58, pp. 2059, 1987”). The photonic crystal is a configuration (structure) forming a permittivity distribution with a period smaller than a wavelength. The method disclosed in the “Physical Review Letters, Vol. 58, pp. 2059, 1987” is to limit a wavelength band of light capable of existing in the vicinity of the active layer by using a property that is a “photonic band gap” which the photonic crystal has, to suppress spontaneous emitted light other than the light at a desired wavelength. In this way, it is desirable to use a three-dimensional photonic crystal forming a three-dimensional permittivity distribution in order to control the spontaneous emission to obtain high luminous efficiency. Further, from the standpoint of an optical confinement effect, it is preferable to use a three-dimensional photonic crystal having a strong optical confinement effect.
Japanese Patent Laid-Open No. 2001-257425 discloses a light emitting device using such a three-dimensional photonic crystal. In the configuration disclosed in Japanese Patent Laid-Open No. 2001-257425, an active layer is formed in the three-dimensional photonic crystal, and carriers are injected into the photonic crystal through a contact layer from a metal electrode provided outside the photonic crystal. The injected carriers are conducted in the configuration of the photonic crystal to be connected to a carrier conducting path formed of a line defect to be guided to an active portion. Moreover, U.S. Pat. No. 5,335,240 and Japanese Patent Laid-Open No. 2005-292787 disclose examples of configurations of the three-dimensional photonic crystal.
In the configuration disclosed in Japanese Patent Laid-Open No. 2001-257425, the carriers injected from the electrode are conducted in the configuration of the photonic crystal. In the configuration disclosed in Japanese Patent Laid-Open No. 2001-257425, since the carriers are conducted inside columnar structures arranged in a hanging rack form, a cross-sectional area of the carrier conducting path is smaller and a length thereof is longer than those in a conventional semiconductor light emitting device. Therefore, a series resistance in the carrier conducting path is increased. This brings about lowering of injection efficiency. This has a significant effect on the P-cladding layer with a lower electric conductivity particularly.
Further, in order to increase the injection efficiency in the light emitting device using the three-dimensional photonic crystal, it is necessary to reduce a thickness of the P-cladding layer. However, reducing the thickness of the P-cladding layer decreases a periodic number of the photonic crystal, which weakens the optical confinement effect.